The invention relates to hard setting refractory compositions and especially to rapid hard setting castable refractory compositions comprising fumed silica and a refractory material, such as one containing alumina, which when mixed with water will set to a hard mass at normal outdoor temperatures without any calcareous cementious material being present in the composition.
Calcareous cements that contain fumed silica and are rapid setting are known as shown in Miller et al Pat. No. 4,501,830. Also, Pat. No. 4,506,025 discloses a castable silica brick composition containing fumed silica, silica and portland cement. This composition is relatively slow setting and contains undesirable calcium oxide compounds. Japanese Patent No. 1981-78476 shows a similar castable composition based on the coagulation of superfine silica powder with the Ca ions of Portland cement.
U.S. Pat. No. 3,121,641 discloses a castable composition containing alumina and fumed silica and U.S. Pat. No. 3,067,050 discloses a gunning mixture containing alumina and fumed silica. However, these compositions do not set quickly to a hard set, and must be given a lengthy curing and then fired to obtain suitable strength and hardness.